Pay-for-usage is the only way to go for bandwidth. We have been spoiled since the Internet came onto the scene in that many companies have gone out of their way to place no restrictions on its use. That's why we get these flat-rate, unlimited plans for home internet usage as well as cellular.
But at the end of the day, what is the difference between megabytes, kilowatt hours, gallons of water, and therms? For the last three of these items, it is standard practice to pay for whatever we use. So if we use more water, natural gas, or electricity, we pay to do so. It's simple.
Yet for some reason people take an entirely different approach when it comes to paying for internet service, where anything short of unlimited data for a low price is seen as a sign of corporate greed. But what is the difference between delivering megabytes and electricity? Both take a lot of capital expenditure to deliver, and a lot of maintenance. They are both commodities. So why would we be perfectly comfortable paying for kilowatt hour usage but not megabyte usage?
The reality is that communications companies are likely scared to death of this just as much as their customers are. If AT&T is right that 98% of their customers use less than 2GB of data per month, then they likely have a lot of people paying for a lot more data than they are actually using. If these companies offered usage-billing like other utilities do, they'd likely see a collapse in revenues. So the "unlimited" plans have actually served these companies very well, I would tend to believe.